Foreman » Smart Proxy

Add to_json method to lease and reservation module

The /dhcp/:network returned strings instead of dicts for
reservation and leases. This patch adds to_json methods
for reservation and lease to return dicts instead of strings.

fixes #1154 - ms dhcp smart proxy error 400

This commit is not ideal in term of performance, as it forces us to read each
reservation options, a probably better approch is to read the output from the
dump command instead.

clean up code passing, and removed duplicate code between dhcp server implementations

Added DHCP as a module